A processor executes a program called a start-up routine when it is booted. Although it depends on the environment in which the processor executes a program, the start-up routine includes processes necessary before the main routine is executed, such as setting a variety of registers, copying minimally necessary programs from a memory device outside the processor into a cache memory, and setting the cache memory to a usable state. A specific example of the setting of a variety of registers is a setting for an external peripheral device connected to the processor, such as a latency setting for a DRAM that is a main memory device.
In many cases, the start-up routine is stored in a nonvolatile memory device outside the processor. A mask ROM, a PROM, an EPROM, a flash memory, or the like is normally used as a nonvolatile memory device for storing the start-up routine. Patent Document 1 discloses a processor which includes a power-on determination circuit for determining whether power has been turned on for a system or for periodic operation and therefore does not require an operation to read table data of initial values from a boot ROM when power has been turned on for the periodic operation.